Leaching nickeliferous oxide ores

Abstract

In leaching a slurry of nickeliferous oxide ore containing less than about 35% iron with sulfuric acid under superatmospheric pressures at temperatures between about 230° C. and about 300° C. a water-soluble alkali metal or ammonium compound is added to the slurry after leaching is more than about 50% complete whereby the settling characteristics of the leached slurry during solids-liquids separation are improved.

I claim: 
     
       1. In a process for recovering nickel from nickeliferous oxide ores containing less than about 35% iron in which the ore is slurried with water, the slurry is preheated to a leaching temperature between about 230° C. and about 300° C., sulfuric acid in an amount between about 0.15 part and about 0.8 part for each part of dry ore is added to the preheated slurry to leach the nickel values from the nickeliferous oxide ores, the leached slurry is neutralized and the neutralized slurry is subjected to a liquids-solids separation operation, the improvement which comprises: adding at least one water-soluble compound selected from the group consisting of alkali metal or ammonium compounds to the slurry when the leaching reactions are more than half complete in small but effective amounts to minimize dissolution of silica, whereby the settling rate of the neutralized slurry is improved. 
     
     
       2. The process as described in claim 1 wherein a high magnesia nickeliferous oxide ore is added to the slurry at the leaching temperature after the leaching reactions are complete to neutralize most of the free acid contained in the leach liquor and to recover a substantial portion of the nickel contained in the high magnesia containing ore. 
     
     
       3. The process as described in claim 1 wherein the leached slurry is cooled and let down to atmospheric pressure and neutralized with fresh high magnesia nickeliferous oxide ore and the residue from neutralization is fed to the leach slurry at the leaching temperature after the leaching reactions are completed. 
     
     
       4. The process as described in claim 1 wherein the amount of water-soluble compound added to the slurry is up to about 5%, based on the dry weight of the ore. 
     
     
       5. The process as described in claim 4 wherein the water-soluble compound is added in amounts between about 0.5% and about 2.5%, based on the dry weight of the ore. 
     
     
       6. The process as described in claim 5 wherein the water-soluble compound is added in amounts between about 1.5% and about 2.5%, based on the dry weight of the ore. 
     
     
       7. The process as described in claim 6 wherein the water-soluble compound is at least one member selected from a group consisting of sodium sulfate, sodium chloride, sodium nitrate, sodium bisulfate, sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium phosphate, sodium silicate, ammonium sulfate, ammonium chloride, ammonium nitrate, ammonium bisulfate, ammonium hydroxide, ammonium phosphate, potassium sulfate, potassium chloride, potassium nitrate, potassium phosphate, potassium silicate and potassium bisulfate. 
     
     
       8. The process as described in claim 7 wherein the water-soluble compound is sodium sulfate. 
     
     
       9. In a process for recovering nickel from nickeliferous oxide ores containing about 37.1% iron in which the ore is slurried with water, the slurry is preheated to leaching temperature between about 230° C. and about 300° C., sulfuric acid in an amount between about 0.15 part and about 0.8 part for each part of dry ore is incrementally added to the preheated slurry to maintain the aluminum content of the slurry at a value of less than about 3 grams per liter to leach the nickel values from the nickeliferous oxide ores, the leached slurry is neutralized and the neutralized slurry is subjected to liquid-solids separation, the improvement which comprises: adding at least one water-soluble compound selected from the group consisting of alkali metal or ammonium compounds to the slurry when the leaching reactions are more than 50% complete in small but effective amounts to minimize dissolution of silica whereby the settling rates of the neutralized slurry is improved. 
     
     
       10. In a process for recovering nickel from nickeliferous oxide ores containing less than about 35% iron in which the ore is slurried with water, the slurry is preheated to leaching temperature between about 230° C. and about 300° C., sulfuric acid in an amount between about 0.15 part and about 0.8 part for each part of dry ore is added to the preheated slurry to leach the nickel values from the nickeliferous oxide ores, the leached slurry is neutralized and the neutralized slurry is subjected to a liquid-solid separation operation, the improvement which comprises: adding at least one water-soluble compound selected from the group consisting of alkali metal or ammonium compounds to the slurry when the leaching reactions are more than about 50% complete in small but effective amounts to minimized dissolution of silica whereby the settling rates of the neutralized slurry is improved. 
     
     
       11. The process as described in claims 9 or 10 wherein the amount of water-soluble compound added to the slurry is up to about 5%, based on the dry weight of the ore. 
     
     
       12. The process as described in claims 9 or 10 wherein the water-soluble compound is added in amounts between about 0.5% and about 2.5% based on the dry weight of the slurry. 
     
     
       13. The process as described in claims 9 or 10 wherein the water-soluble slurry compound is sodium sulfate.